Читать книгу A Book of Nimble Beasts - Douglas English - Страница 5

This is Toad's Spawn, which is laid in "Ropes"

HOW many of you can tell me the difference between a frog-tadpole and a toad-tadpole? I don't mean when they are so small that it seems a kindness to call them tadpoles at all, but when they are quite a good size, with great fat heads and shiny little eyes and squiggly little tails. And how many of you can tell me the number of different kinds of tadpoles which one can find in England in the springtime? Most of you, I am sure, know a tadpole when you see one (sometimes he is called "pot-ladle,"or "polly-wog," or "horse-nail,") and some of you may know that a fat frog-tadpole is brown with little specks of gold, while a fat toad-tadpole is black all over; but I don't expect many of you know that there are two kinds of frog-tadpole, and two kinds of toad-tadpole, and three kinds of newt-tadpole, to be met with in England, which makes seven kinds of tadpoles in all.

Now as these seven little tadpoles are all different from one another (though the two frog-tadpoles and the two toad-tadpoles are not very different), we may be quite sure that they grow up into seven different little beasties. I am going to tell you something about the frog- and toad-tadpoles now and leave the newt-tadpoles for another time, for it will be easier for you if you don't have too much to remember at once.

If you go into the country in springtime (the middle of March is the best time where I live, but in other places it may be a little earlier or a little later) and find a pond, or a brook which runs quite slowly, or even a hole in swampy ground which has water in it, you are almost sure to see a lump of stuff which looks like dirty grey jelly, either close to the bank or on the top of some of the weeds.

If you pick up a little of this, you will find (perhaps before it has slipped out of your fingers and perhaps after) that it is full of round black eggs.

This is Frog's Spawn Floating on the Water

The grey jelly is either frog's spawn or toad's spawn.

If it is just a lump with no particular shape to it, it is frog's spawn, but if it is made up of small slimy ropes, which come apart from one another, and in which the eggs lie in rows like strings of black beads, it is toad's spawn. When you find toad's spawn, you may be sure that frog's spawn has been about for some time, for frog's spawn is always to be found rather earlier in the year. Whichever it may be you should take a little of it (quite a little is best) and put it in a glass jam-jar half full of water, and stand this in some bright, warm place, where it will not get knocked over, and where the sun will not shine directly on to it.

Frogs and toads usually lay their eggs in places where the sun does shine on them and warms them gently, and so hatches them out, but of course they do not lay them in glass bottles, and if the sun shines on these, the water will get warmer than is good for them, partly because there is no other water round to keep it cool, and partly because the bottle acts as a kind of burning-glass, and brings too much of the sunshine into itself, and so gives too much warmth to the eggs.

Some people think the jelly of frog's or toad's spawn acts like a burning-glass too; this, however, is a burning-glass which Mother Nature has arranged, and so there is no fear of its not acting properly.

This is Frog's Spawn When it is Quite Fresh

If you find frog's or toad's spawn soon after it is laid, you will see only a small quantity of jelly round it, but this soon swells out and gets much bigger.

This is Frog's Spawn, too

But I have photographed it with a microscope, so that you may see it a little bigger than it really is. Right in the middle is a Tadpole who has grown his feathery gills, and close to him is one like a little alderman. There is another Tadpole with gills towards the right hand bottom corner, but there is an egg behind which makes his shape wrong. All the round things are eggs and the long things are Tadpoles which have just hatched

Frog's Spawn

The Little Curly Tails are beginning to Grow

Have you ever seen Cook make a jelly? The first thing she does is to soak the gelatine in water, so that it gets soft and swells to twice the size it was before. It swells because it takes up water inside it, and frog's spawn does just the same. Now we must try and think what the frog's spawn jelly is for. It is really the white of the eggs, the black beads being the yolk. You wouldn't understand all its uses, but one is that it makes the frog's spawn much more difficult to eat, because it is so slippery. A great many water birds are very fond of frog's spawn and would gobble it up very quickly if they had a good, big spoon, instead of a rather small bill. As it is, a great deal of frog's spawn and a good many tadpoles are eaten up one way or another, which is really rather lucky for us, for frogs and toads lay millions and millions of eggs, and, if they all hatched out, there wouldn't be room in the world for all little frogs and toads.

The Tadpoles are here seen Getting very like Frogs

Most of them have all four legs, but one has only his hind legs at present

Well, if you keep your glass bottle with the eggs in it in a good place and look at it every day, you will find something fresh to interest you every day. First the black yolks will grow larger and change their shape so that they seem longer than they are broad, and presently you will find that they are turning into tadpoles. The baby tadpole seems much too fat to begin with, and sticks out in front like a little alderman; but soon he gets slimmer again, and you find that he is growing a curly tail (which no alderman ever did), and that there are tiny markings where his eyes and mouth are going to be. He is still very small (about a quarter of an inch long), but before he is much bigger a very wonderful thing happens—it has been happening all the time, though you have not been able to see it—he grows a pair of gills like a fish. They are delicate, feathery things, and stand out on either side of his head, I should like to say "neck," but I do not think I ought to because frogs and toads have no necks at all, and so I suppose tadpoles have none either. All this time his tail is growing too, and presently it is long enough for him to swim with. When this happens he slips out of the jelly and wriggles about in the water. At present he has no real mouth, but he has a little opening, shaped like a horseshoe, near to where his mouth is going to be, and he uses this to hold on to weeds when he is tired, which he very soon is at first.

Once he is fairly hatched, however, his mouth grows quickly and he gets a pair of rather hard little jaws with which he can nibble the water-weed. When this happens you must, of course, put some water-weed into the bottle, though grass will do if you can't get anything else.

Tadpoles Full Grown

They are covered with little specks of gold. At the bottom one can be seen feeding

I told you that he had gills like a fish, but they are curious gills at this early stage because they have no flap of skin to protect them. If you want to see a fish's gills you must lift up the hard flap of skin which covers them. The tadpole soon grows a flap of skin, though, just like a fish, and this always appears first on the right side, so that at one stage he looks as if he had only one gill, the one on the left side. When both the flaps of skin have grown, the tadpole is really a little fish, and he stays in much the same shape, though he gets fatter and fatter, for about a month. At the end of this time he begins to grow legs, first the hind ones and then the front ones (newt-tadpoles grow the front ones first); but, in spite of his legs, he is still only a fish, because, instead of breathing the air with his lungs as a grown-up frog does, he breathes the water with his gills. During the next month, when he is getting on for three months old, another wonderful change comes over him. For a time he breathes both with his lungs (he has to put his head out of water for this) and with his gills, and so he is both a frog and a fish at once; but he gets more and more like a frog, and less and less like a fish. His lungs keep growing inside him, and his body and gills and tail get smaller and smaller, and his mouth and his eyes and his legs get larger and larger, and presently he leaves the water altogether, for he is tired of water-weeds and tired of his tail (he can swim beautifully without it), and he wants to make his meals off insects and slugs, and to learn how to croak and jump, and to be a great fat frog like Mother.